Blank screen on client connect - frequently

Currently SC Cloud and running latest 26.6.6.9747 - frequently getting blank displays on connect and it will not display the current desktop (across many client environments) - sometimes a CTL/ATL/DEL pops up the display - sometimes a reboot is the only way to get it working but disrupts client work. Perhaps 15% (guess) of the time this seems to happen - single displays, mutiple displays does not seem to matter.